(a) Field of Invention
The present invention relates to a system which includes a master station and a plurality of slave station. The present invention is useful as a building maintenance system. The system is capable of executing application method at the slave stations in accordance with application methods at the slave stations in accordance with instructions previously transmitted from the master station. The system is also particularly designed as a backup processing system to backup the master station when it fails.
(b) Description of the Related Art
FIG. 1 is a block diagram of a building maintenance system of the prior art. In FIG. 1, 1 designates a master station and 2-1, 2-2, . . . , 2-n, designate slave stations. The master station 1 and the slave stations 2-1, 2-2, . . . , 2-n are mutually connected through communication line 3.
Master station 1 receives particularly important data such as the power failure/power recovery signals and fire/extinguishing signals from building common facilities 4. The slave stations 2-1, 2-2, . . . , 2-n send control signals to the devices 5, such as air-conditioning facilities, lighting facilities and so forth, and receive operation information from these devices.
Particular building maintanance data 4', such as temperature and humidity of open air and seasonal mode, i.e., four-season (spring, summer, autumn and winter) information, is input to the nearest slave station (for example, 2-1). The master station 1 is connected with a display unit 6 and keyboard 7 or printer 8.
In such a system, the application programs which are processed in the master station are also processed in the slave stations for dispersion of the risk of failure of the processor (CPU) in the master station 1 and failure of the master station 1 itself. Namely, the master station 1 previously loads the schedule data to respective slave stations 2-1, 2-2, . . . , 2-n to control the ON/OFF state of devices 5 at predetermined times based on the schedule data received from the master station 1. Such control is called the schedule ON/OFF control.
An operation flowchart of the operations of the slave station for the schedule ON/OFF control of the prior art is shown in FIG. 2. In case the master station 1 is operating normally, the NO route is selected in the step a1. Therefore, the slave stations 2-1, 2-2, . . . , 2-n store or set the system common data sent from the master station 1 as stored data in step a2. In step a3, to execute the application function is executed based on the stored data.
However, if the master station 1 fails, the prior art described above does not distribute the system common data which is fetched only in the master station 1 to the slave stations 2-1, 2-2, . . . , 2-n. Therefore, the application programs in the slave stations 2-1, 2-2, . . . , 2-n continue the processings based on the data last distributed by the master station 1 (refer to the YES route of step a1 in FIG. 2), resulting in the following problems.
If a fire breaks out in the building while the master station 1 is defective, the devices 5 for air-conditioning must be stopped, as a rule, during the fire. However, this cannot be achieved since the fire information is not extended to the slave stations 2-1, 2-2, . . . , 2-n when the master station 1 fails. It is probable that the slave stations may even start the devices 5 on the basis of the stored data last received from the master station 1.
If the master station 1 stops while temperature and humidity control for the air-conditioning are carried out in the slave stations, the master station 1 no longer collects maintanance data for air-conditioning of the external air, humidity and seasonal mode. As a result, the maintenance data for air-conditioning is no longer distributed from the master station 1, such data is generally input only from the one inlet to the system and it is therefore essential for safe and effective control of the air-conditioning system. If supply of such data stops, then the slave station can only continue the processing with the lastest data received from the master station 1. Hence, it is no longer possible to execute the control in accordance with the environmental condition. It is also undesirable from the point of view of energy, conservation.